Inefficiencies in the quantity of refrigerant (too much or too little) is a major cause of compressor failure in air condition systems and can increase the energy cost for operating the air conditioning system, for example, increasing fuel use in a vehicle or electrical use in a structure. Running an air conditioning system on low refrigerant can result in compression failure due to low lubrication levels (delivered with refrigerant). Running an air conditioning system with too much refrigerant can result in compression failure due to blow out or other issues.
Recharging air conditioning systems, such as motor vehicle air conditioning systems, requires adding or removing refrigerant from a low pressure and/or high pressure sides of the air conditioning system. Most modern vehicle air conditioning systems are equipped with a thermal expansion valve and temperature sensor bulb which controls the rate of flow of liquid refrigerant into the evaporator (low pressure side) and which sets the maximum operating pressure. When recharging the low pressure and/or high pressure sides of a system, care must be taken not to overcharge the system and create potentially damaging or explosive situations.